Battery charger

ABSTRACT

A battery charger for charging batteries that may have a nominal rated voltage equal to or greater than the voltage of the source, includes an accumulator of energy such as an inductor which is coupled across the source through a controllable switch for a first selected interval of time. The charger further includes a path between the accumulator of energy and the battery to be charged for the transfer of the stored energy to the battery. The path between the accumulator and the battery advantageously includes a unilateral impedance element having a recovery time such that a discharge path is provided for the battery during a second selected interval of time substantially less than the first selected interval of time.

Carlsen, II

[ 4] BATTERY CHARGER [75] inventor: George David Carlsen, I], Playa DelRey, Calif.

[73] Assignee: McCulloch Corporation, Los

Angeles, Calif.

[22] Filed: June 9, 1971 1211 Appl. No.: 151,447

[52] US. Cl 320/21, 320/39, 321/2 [51] Int. Cl. H02j 7/10 [58] Field ofSearch 320/8, 2-6,

320/21, 61, DIG. 2, 39, 40; 322/2, 28; 321/2 [56] References Cited V vUNITED STATES PATENTS 3,629,681 1 12/1971 Gurwicz 320/21 x 3,384,8065/1968 Hartman; 322/28 x 3,594,627 7 1971 1.651161 321 2 x 3,597,673 81971 Burkett 320/21 x 3,305,755 2/1967 Walsh 320/21 x PrimaryExaminer-J. D. Miller Assistant Examiner-Robert J. HickeyAttorney-Christie, Parker and Hale [5 7] ABSTRACT A battery charger forcharging batteries that may have a nominal rated voltage equal to orgreater than the voltage of the source, includes an accumulator ofenergy such as an inductor which is coupled across the source through acontrollable switch for a first selected interval of time. The chargerfurther includes a path between the accumulator of energy and thebattery to be charged for the transfer of the stored energy to thebattery. The path between the accumulator and the battery advantageouslyincludes a unilateral impedance element having a recovery time such thata discharge path is provided for thebattery during a sec- 0nd selectedinterval of time substantially less than th first selected interval oftime.

6 Claims, 1 Drawing Figure BATTERY CHARGER it CROSS" REFERENCE TO =RELAT ED APPLICATIONS accumulator is connected in*-serieswith the*source'anii the series cornbination-isconnected'tothe" battery'to' be 'chargedand the stored--energy is transferred tothe'b'atte'ry. Thestoring-ofenergydnthe accumulatorand the .claimed in U. S.'Pat. No.3,5l'7,293 issued June 2 3, I970, copending US. application Ser. No. 1867 3838 minedbythe components of the'oscillatortoprogressivelychargethe battery. The" charger -mayfurther'advantageou'slyinclude means forterminating the *charging of "the battery, :wvhic'h*means comprises ci'rc'u'it 24, 1969, now U.'S.'Pat. No; 3;609,502,.-granted1'Sept. 10-meansformonitoringthe'terminal'voltage*an'dcircuit28, 197 1 all of which are assignedtothesame assignee as thisapplication.

BACKGROUND OF THE mvEfNTIoN 1. Field of the Invention I This inventionrelates to a 'method and-apparatusfor charging batteriesfrom a' source.thatmay'havea terminal voltage-equal to or less thanthe'nominalratedvoltage of the battery to be chargedand also-.=tothe-rapidcharging of batteries from such asource.

With the increased use of batteries togpowerdevices, the charging ofthe-batteries =hasbecome morefl-rimportant. Often times the mostdesirablesource of charging current is not immediately :available:and-tthe*batteries have to be charged from a less desirable'source. Forexample, tape players maybe-carried to-remote locations by automobile sothat the only-source of :charging current available is the 12voltautomobile-battery.orthe 12 volt generator of the automobile. lloweven insome cases the-batteriespowering the portable device such as atape player have. a nominal rated voltage of 12 volts or greater so thatdirect charging from'the automobile battery .is not possible. However,the ability to charge a battery from alower voltage source is desirable.Moreover the rapid charging of a higher voltage battery from a lowervoltage is desirable-so that thebattery powered device may be put backinto service as soon as possible.

SUMMARY OF THE INVENTION In accordance with the present invention,sourcesof charging current having voltages that may be lower than thevoltage of the battery to be charged are advantageously employable tocharge batteries. in particular it is possible tocharge a battery havinga 'nominal voltage rating that is equal to or greater than the voltageof the source by the method and apparatus of this invention.Additionally, the charger of thisinvention islight weight and compactand may be easily housed in *the housing for the battery powered device,such-as a'tape i lator having two active elements,'one of-which functions as a switch to connect the accumulator directly across the sourcein one mode of operation. In the second mode of operation the switch isopen so that the 'means' responsive *to the monitorin'g means forinhibiting thero'scillator 'u'po'n "-'t hega'ttainment of "a predeterrnine'd voltage at' theterminals of'the" battery. Addition- :allyfithecharger may include an indicator flightope'ra- Ebledn respohsetdtheoscillatortoindicatethe-applicactirrent'tO the *battery FHe chaBgermaytfurtherinclude circuitmeans for compensatingforyva'riations:in"='the voltage of the source'sothat charging is'rterminate'd at a higher battery voltage "*for higher asourcevoltagesandatlower battery voltages =forlower source voltages.

BRIEF DESGRIPTIQN :OF THE IDRAWINGS Theabove and other features andadvantages of the fpresent invention may be understood more clearly andfully :upon consi'deration of the following specification arfd drawinginwhich the singleIGURE is a-sche'ma tic :diagram of an apparatus forcharging a battery from a source Whichmay "have a voltage below thenominal rated voltage -'of the -battery*tobe charged in accordance-wi'th"'the' present' invention.

DESCRIPTION 0F THE PREFERRED EMBODIMENT I An apparatus capableofchaiging a batteryffrom a source -which may"have,-a voltage lower thanthe nominal'rated voltage'o'f the battery to be charged is schematicallyshown in' the single FIGURE of the drawing. The apparatus of: the:drawing includes two partssepa- "rated *by the dotted line.Thep'orti'on of the apparatus to the right of thedotted line is used incharging the "'battery, while the portion to the left of "the dottedline isemployedto automatically terminate thecharging of the batteryupon the-attainment of apredetermined value of battery terminal voltage.

The apparatus for charging a battery 1 from a'source Zincludes anoscillator3. The oscillator 3 has two active elements,aPNP transistor 4and an NPN transistor 5. Theemitter of transistor 4 is connected to thepositive terminal-'o'fthe source 2. The co'llector of transistor risconnected through aresistor '6 and a resistor '7 in series tothenegative'terminal 'ofsou'r'ce '2'. Forpurtery to be charged so that theenergy stored in the accumulator is transferred to thebattery to chargethe battery. The control circuit of the charger may be an oscil:

poses of illustration it-is assumed that the negative terminal of source"2' is connected to ground reference.

However, it is tobeunde'rst'ood that the positive terminal of'the sourcemay be connected to ground reference-or it hat'neither terminal isconnected to ground the apparatus for charging the battery 1 t Theoscillator 3-further-includes a feedback network reference withdirectconnections then being made to ofa resistor-8 and a capacitor9connected in series be 'vi'der network of a-resistor lo conne'cted inseries with a resistor =11 between the positive and negative terminals0f thesource Zfor providingbiasiorth'e'transistor 4. Forthis-purpose thebaseof' transistor 4 is connected 3 to the junction of resistors and11."As a further part of the oscillator 3, an inductor 12 is connectedbetween the collector of transistor 5 and the positive terminal ofsource 2. The bottom terminal of inductor 12, which is connected to thecollector of transistor 5, is also connected to the positive terminal ofthe battery 1 to be charged througha diode 13. The cathode of diode 13is connected to the positive terminal of the battery 1 while the anodeis connected to theinductor 12.

The apparatus further includes a diode 14 connected between the base oftransistor 4 and the positive terminal of the source 2. The negativeterminal of the battery 1 is connected to the negative terminal of thesource 2, Y

which connection is representatively shown by the connection to groundreference in the drawing.

In operation the inductor 12 functions as an accumulator of energy or ameans for storing energy in the following manner. The voltage of source2 is applied to theapparatus by some suitable means such as the closingof a switch (not shown) or the connecting of a line from the charger toan automobile battery, e.g.,

through a cigarette lighter outlet. In any event, upon the applicationof the voltage from the source 2, transistor 4 will be biased on by theappearance of a negative voltage at its base with respect to itsemitter. The

negative voltage at the base with respect to the emitter of transistor 4is developed across resistor 10, which is in series with resistor 11 andtogether form a voltage divider across the source 2. Current flowthrough transistor 4 will pass through resistors 6 and 7 to bias ontransistor 5. As current begins to flow through transistor 5, the seriescombination of relatively low resistance resistor 8 inseries withcapacitor 9 presents a relatively low resistance pathin parallel withresistor 11 so that more voltage is dropped across resistor 10 toincrease conduction through transistor 4. Sufficient bias is eventuallyprovided by the conduction of current through transistor 4 and resistors6and 7 to drive tran sistor 5 into saturation. Thus, transistor 5functions essentially as an electronic switch and point A, to whichinductor 12, diode 13,-capacitor 9, and the collector of transistor 5are connected is held essentially at ground reference while transistor 5is conducting.

During this time current willflow from the positive terminal of source 2through inductor 12 to store energy in the magnetic field of inductor12. There will be no current path through diode 13 to battery 1 duringthis interval of time because saturation of transistor 5 effectivelyshort circuits this current path. Addition-.

current flowing. Upon the cessation of current flow through inductor 12,the polarity of the voltageacross' the inductor will change and thevoltage induced by the self-inductance will present-a positive potentialat point A. The voltage developed across inductor 12 will add to thevoltage of source 2 such that the positivevoltage of the'battery l.Diode 13 will thus be forward biased and the energy stored in inductor12 will be transferred through diode 13 to the battery 1 to cha gethebattery. As the voltage of point A with respect to groundreferencedecreases below the voltage of the battery 1, the diode 13 willbecome back biased again. Capacitor 9 will during this time dischargethrough resistor 8, diode 14, and inductor 12. The magneticfield aroundinductor 12 willcontinue to collapse, inducing a voltage in theinductor, until transistor 5 isagain turned on or the energy remaininginthe inductor 12 after the back biasing of diode 13 is transferred tocapacitor 9 and resistor 8. Upon the back biasing of diode 13, increasedcurrent will flow through resistorsl0 and 11 to again bias transistor4on and the cycle will be repeated.

An indicator lamp 15' is connected across resistor 6 so that as thecycle repeats, the indicator lamp will be illuminated so that theoperation of the apparatus may be visually monitored. The cycles mayberepeated for a preselected interval of time or until one of the chargeconditions of the battery attains a predetermined value.

Apparatus for monitoring one of the charge conditions, in particular theterminal voltage of the battery 1 being charged, is shown in the lefthand portion of the drawing. The apparatus for terminating the chargingof the battery 1 includes a means for monitoring the terminal voltage,which comprises a Zener diode 20 connected in series with apotentiometer 21 across the terminals of the battery 1. Circuit meansresponsive to the monitoring circuit means is also included in theapparatus for terminatingthe charging of the battery 1. This circuitmeans includes a silicon controlled rectifier 22 connected in serieswith a resistor 23, a resistor 28, and a resistor 24 between thepositive and negative terminals of the source 2. Resistor. 28 andresistor 23 are connected in series between the anode of rectifier 22and the positive terminal of source 2 with one side of resistor 23 beingconnected to the positive source. Re-

sistor 24 is connected between the cathode of rectifier 22 and thenegative terminal of source 2. A transistor 25, which functions as anelectronic switch under the control of silicon controlledv rectifier 22,forms a part of the apparatus for terminating the charging of thebattery 1. The emitter of transistor 25 is connected to the positiveterminal of source 2, while the collector is connected to the base oftransistor 4 so that the emitter collector path of transistor 25 isdirectly across the bias resistor 10 which controls the operation oftransistor 4. The base of transistor 25 is connected to the junction ofresistor 23 and resistor 28. Y

The operation of rectifier 22 is controlled by the voltage which appearsbetween the movable arm of potentiometer 21 and ground reference, whichvoltage is representative of the terminal voltage of the battery 1. Thegate of rectifier 22 is connected through a resistor 26 to the movablearm of potentiometer 21. A capacitor 27 is connected between the gate ofrectifier 22 and the negative terminal of source 2 and cooperates withresisat point A will be substantially in excess of the voltage tor26 toform a filter circuit which bypasses unwanted voltage variations so thatthe apparatus for terminating the charging of the battery is responsiveonly to the terminal voltage of the battery and not some spuriousvoltages.

In operation the Zener diode 20 has a selected breakdown voltage wherebythe terminal voltage of the batte'ry 1 must be above a predeterminedvalue before any current'y/ill flow through Zener diode 20 andpotentiometer ZLThereafter as the terminal voltage of the battery 1increases, the voltage on the gate of rectifier 22 with respect to itscathode will increase until a predetermined value is reached. At thispredetermined value, the rectifier 22 will be turned on and current flowthrough current limiting resistor 28 and resistor 23 will biastransistor 25 on. The turning on of transistor 25 will bypass resistorl0,thereby inhibiting the oscillator 3 by removing the bias fortransistor ,4 and the charging of the battery 1 is terminated.

The, apparatus for charging av battery shown in the drawing includes avoltage compensation circuit to compensate for variations in sourcevoltage. The compensation circuit includes resistor 30 connectedinseries with resistor 31, which series connection is connected betweenthe positive and negative terminals of the source 2. A diode 32 isconnected between the junction of resistors 30 and 3 1 and the cathodeof silicon controlled rectifier 22. Thereafter as the voltage of thesource-2 varies, the voltage at the cathode of silicon tier 22 willincrease and a higher voltage on the gate of the rectifier 22 will berequired to turn this rectifier on. Thus, a higher terminal voltageacross battery 1 will be required before charging is terminated.

The method of charging aibattery in. accordance with this invention froma source having. a voltage which may be less than the nominal ratedvoltage of the battery to be charged comprises the steps of storingenergy from a source in an accumulator of energy during a first intervalof time, transferring a portion of the stored energy to the battery tobe charged during a second interval of time, and repeating the steps toprogressively charge the battery. The method may further include thestep of discontinuing the cycles after a preselected interval of time,or automatically terminating the cycles in response to the attainment ofa predetermined value of a. battery condition. lnparticular the methodmay further comprise the steps of monitoring the terminal voltage of thebattery and terminating the charging in response to the attainment of apredetermined value of terminal voltage. This method of charging abattery was accomplished by use of the apparatus of the drawing in onenon-limiting example where the components of the apparatus had thefollowing identification or values.

Battery 1 sub C cells having a rated capacity of 1 amp hour and anominal rated voltage of 12 volts.

Source 2 12 volt automotive battery.

Transistor 4 Motorola 2N49l8.

Transistor 5 Motorola 2N377l.

Resistor 6 16 ohms.

Resistor 7 12 ohms.

Resistor 8 132 ohms.

Capacitor 9 0.47 microfarad.

Resistor l0 1,000 ohms.

Resistor ll 10,000 ohms.

Inductor l2 ll5 microhenrys.

Diode l3 Two Motorola 1N400l (a pair are employed for economy reasons. Asingle one may be employed.)

Diode 14 Motorola lN9l4.

indicator Lamp 15 3.2 volt, 160 milliamp bulb.

While employing these components in the apparatus of the drawing, thecurrent through inductor l2 in-- creased from 0 amperes to approximately18 amperes while transistor 5 was in saturation. Upon the shutting offof transistor 5, the energy stored in inductor 12 was transferred to'the10 sub C cells .of the battery 1 with a peak current of 10 amperes andan average current during the interval of time that current flowed intobattery l of 4 amperes. This average charge current is thusapproximately four times the nominal 1 hour rate of the cells of thebattery. The nominal 1 hour rate in this application is defined as thenominal rate of the discharge current for one hour to a select endvoltage such as one volt per cell, as established by the manufacturer ofthe cells. A type sub C cell is normally rated at l ampere hours andthus has a C rate or a nominal 1 hour rate of l ampere. An averagecharge current of 4 amperes, which is inexcess of the nominal 1 hourrate of the cells tery. Upon the. decrease of the self-induced voltageof inductor 12 to back bias diode 13 and the turning on of transistor 5-at the end of the charge interval, a discharge pulse through diode 13may selectively occur. This discharge pulse is a consequence of therecovery time of diode 1'3 and is believed to enhance the ability of thebattery 1 to accept the high rate charge. While applying an averagecharge current of 4 amperes to the 10 subC cell batteries andintermittently discharging through the diode 13, the battery I wascharged to a selected state of charge in 15 minutes. The selected stateof charge was; substantially the rated: capacity of the battery. Theselectedistate of charge was determined by monitoring the terminalvoltage of the battery 1'. For the 12 volt battery, the terminal voltagewas permitted to rise to 15.8 volts, at which point charging wasautomatically terminated.

The apparatus of the drawing is not limited to the charging of batteriesfrom a source having a voltage equal to the'nominal rated voltage of thebatteries, but may advantageously be employed in charging batteries thathave a nominal rated" voltage substantially in excess' of the voltage ofthe source. For example the apparatus has been employed 'tochargebatteries having a nominal rated voltage of 15 volts when the source hada voltage of 12 volts and for charging batteries having a nominal ratedvoltage of 24 volts when the source had a voltage of 12 volts.

Various changes may be made inthe details of construction withoutdeparting from the spirit'and scope of the invention as defined by theappended claims.

What is claimed is: .1; An electrical circuit for charging a batterycomprising ablocking diode;

an inductor connectible in series with the diode between a voltagesource and a battery to be charged;

with the diode being connected on the battery side of the circuit andpoled to block current flow from the battery into the circuit;

a;,timing capacitor network connected across the inductor through asecond blocking diode;

an electronic switch having an ON-state and an OFF- state connectedto'provide when in its ON-state'a' charge current path therethrough forthe capacitor of the timing capacitor network and a current path throughthe inductor from asource, while'bypassing the battery; and a controlcircuit including the timing capacitor network and the inductorfor'alternately switching the electronic switch off and on.

2. An electrical circuit in accordance with claim 1 wherein the controlcircuit switches the electronic switch off upon the capacitor attaininga preselected voltage.

3; An electrical circuit in accordance with claim, 1 wherein the controlcircuit switches the electronic switch on when the second blocking diodebecomes reverse biased.

4. Apparatus for charging a battery from a source comprising anNPNtransistor, a PNP transistor, an'inductor connected in series withthe collector emitter path of the NPN transistor between-the positiveand negative terminal of the source, the inductor being connectedbetween the collector of the NPN transistor and the positive terminal ofthe source, a first resistor connected between the collector of the PNPtransistor and the base of the NPN transistor, means for connecting theemitter of the PNP transistor to the positive terminal of the source, asecond resistor connected between the base of the NPN transistor and thenegative terminal of the source, a voltage divider of a third and fourthresistor connected between the positive and negative terminals of thesource, the base of thePNP transistor being connected to the junction ofthe third and fourth resistor, a fifth resistor and a capacitorconnected in series between the base of the PNP transistor and thecollector of the NPN transistor, a first diode connected between thecollector of the NPN transistor and the positive terminal of the batteryto be charged, a second diode connected .betweenthe base of the PNPtransistor and the positive terminal of the source and means forconnecting the negative terminal of the battery to be charged tothenegative terminal of the source.

5. Apparatus in accordance with claim 4 further including a second PNPtransistor having its emitter connected to the positive terminal of thesource and its collector connected to the base of the first PNPtransistor, a sixth resistor connected between the base of the secondPNP transistor and the positive terminal of the source, a siliconcontrolled rectifier, a seventh resistor, the anode of the rectifierbeing connected to the base of the second PNP transistor through theseventh resistor, an eighth resistor being connected between the cathodeof the rectifier and the negative terminal of the source, a Zener diodeand a potentiometer connected in series between the positive andnegative terminals of the battery to be charged, a ninth resistor beingconnected between the gate electrode of the rectifier and the movablearm of the potentiometer and a capacitor being connected between thegate electrode of the rec tifier and the negative terminal of thesource.

6. Apparatus in accordance with claim 5 further including a tenthresistor and an eleventh resistor connected in series between thepositive and negative terminal of the source and a third diode connectedbetween the junction of the tenth and eleventh resistors and the cathodeof the rectifier.

1. An electrical circuit for charging a battery comprising a blockingdiode; an inductor connectible in series with the diode between avoltage source and a battery to be charged, with the diode beingconnected on the battery side of the circuit and poled to block currentflow from the battery into the circuit; a timing capacitor networkconnected across the inductor through a second blocking diode; anelectronic switch having an ON-state and an OFF-state connected toprovide when in its ON-state a charge current path therethrough for thecapacitor of the timing capacitor network and a current path through theinductor from a source, while bypassing the battery; and a controlcircuit including the timing capacitor network and the inductor foralternately switching the electronic switch off and on.
 2. An electricalcircuit in accordance with claim 1 wherein the control circuit switchesthe electronic switch off upon the capacitor attaining a preselectedvoltage.
 3. An electrical circuit in accordance with claim 1 wherein thecontrol circuit switches the electronic switch on when the secondblocking diode becomes reverse biased.
 4. Apparatus for charging abattery from a source comprising an NPN transistor, a PNP transistor, aninductor connected in series with the collector emitter path of the NPNtransistor between the positive and negative terminal of the source, theinductor being connected between the collector of the NPN transistor andthe positive terminal of the source, a first resistor connected betweenthe collector of the PNP transistor and the base of the NPN transistor,means for connecting the emitter of the PNP transistor to the positiveterminal of the source, a second resistor connected between the base ofthe NPN transistor and the negative terminal of the source, a voltagedivider of a third and fourth resistor connected between the positiveand negative terminals of the source, the base of the PNP transistorbeing connected to the junction of the third and fourth resistor, afifth resistor and a capacitor connected in series between the base ofthe PNP transistor and the collector of the NPN transistor, a firstdiode connected between the collector of the NPN transistor and thepositive terminal of the battery to be charged, a second diode connectedbetween the base of the PNP transistor and the positive terminal of thesource and means for connecting the negative terminal of thE battery tobe charged to the negative terminal of the source.
 5. Apparatus inaccordance with claim 4 further including a second PNP transistor havingits emitter connected to the positive terminal of the source and itscollector connected to the base of the first PNP transistor, a sixthresistor connected between the base of the second PNP transistor and thepositive terminal of the source, a silicon controlled rectifier, aseventh resistor, the anode of the rectifier being connected to the baseof the second PNP transistor through the seventh resistor, an eighthresistor being connected between the cathode of the rectifier and thenegative terminal of the source, a Zener diode and a potentiometerconnected in series between the positive and negative terminals of thebattery to be charged, a ninth resistor being connected between the gateelectrode of the rectifier and the movable arm of the potentiometer anda capacitor being connected between the gate electrode of the rectifierand the negative terminal of the source.
 6. Apparatus in accordance withclaim 5 further including a tenth resistor and an eleventh resistorconnected in series between the positive and negative terminal of thesource and a third diode connected between the junction of the tenth andeleventh resistors and the cathode of the rectifier.